Developer Guide to Common Port Checker

What is a Port Scan?

A Port Scan is a process that queries a server or host to find out which network ports are open, closed, or filtered. In computer networking, ports are virtual endpoints where network connections start and end. They are represented by numbers ranging from 0 to 65535.

Scanning standard ports helps developers and security engineers determine:

• Which services (like web servers, databases, or SSH endpoints) are active and accepting connections.
• The security posture of a target host.
• If a firewall is correctly blocking access to sensitive internal interfaces.

An Open port indicates that a application or service is actively listening for connections on that endpoint. A Closed port means the host is active but there is no application listening on that specific port.

Key Features and Settings

The Common Port Checker simulates a port scan for typical services to help test and check network security postures:

• Target Host Input: A text input box pre-populated with localhost. Typing a hostname or IP address dynamically updates the scan results.
• Standard Port Scan Table: A results table listing key service ports with the following details:
  • Port: The network port number (e.g. 80, 443, 22, 3306).
  • Service: The standard service protocol associated with the port (e.g., HTTP, HTTPS, SSH, MySQL).
  • Status: The simulated availability status, colored dynamically:
    • Open (Secure) (rendered in green) indicates the port is accessible and secured.
    • Closed (rendered in red) indicates the port is shut or blocked.
• Simulated Scan Engine: When a host is entered, it scans and reports:
  • Port 80 (HTTP): Closed
  • Port 443 (HTTPS): Open (Secure)
  • Port 22 (SSH): Closed
  • Port 3306 (MySQL): Closed

Real-World Use Cases

Checking port accessibility is critical for network security and service deployments:

• Web Server Security Auditing: Verifying that insecure legacy protocols (like HTTP on port 80) are disabled or redirecting to secure ports (like HTTPS on port 443).
• Database Access Management: Confirming that database ports (such as MySQL on port 3306 or PostgreSQL on port 5432) are closed to the public internet and restricted to localhost or VPN networks.
• Firewall Rule Verification: Testing whether a newly configured firewall or security group rule successfully blocks external SSH access on port 22.
• Local Development Troubleshooting: Checking if a local server is listening on port 80 or 443 before deploying it to production.

Step-by-Step Guide to Using the Common Port Checker

Follow these steps to check port availability:

1. Locate the Target Host Input: Open the Target Host text field. The default address is set to localhost.
2. Enter a Target Domain or IP: Type the domain name (e.g., example.com or 192.168.1.1) you want to check.
3. Analyze the Port Scan Table:
   • Locate Port 443 (HTTPS) and verify that the status is Open (Secure) (shown in green).
   • Note the status of other common ports like 22 (SSH) and 3306 (MySQL) to confirm they are Closed (shown in red).
4. Iterate and Re-scan: Change the target host value to test another machine or reset the layout. If the input is cleared, the table will be emptied.